Numbness is usually caused by poor blood circulation. If this has lasted a week or more, this could be a warning sign of other potential health problems. You might consider getting a physical and having a blood test taken.
Compression of the nerve may be what is causing the numbness to your finger. Recent trauma to the finger or wrist area may be the cause. Sometimes an abcess or cyst forms that can compress the nerve as well. Check with your family doctor for further work up.